The San Marcos River is the town's main reason to exist as a destination. It rises from the springs at Spring Lake and runs clear through town, with easy places to swim, tube, paddle, or sit under the trees.
Rio Vista Park is the most useful first stop. The old dam has been reshaped into a small whitewater course, so you get a mix of swimmers, tubers, kayakers, and families using the lawns and picnic areas. It is busy in summer, but it is also the quickest way to understand why people here talk about the river as if it were the town square.